The present invention is directed to a waste stripping station in a machine that die-cuts plate-like workpieces, such as sheets of paper or cardboard.
A machine which die-cuts one or more blanks in a sheet of paper, which blanks are then folded and glued to form folded box blanks, is disclosed in U.S. Pat. No. 3,060,776, whose disclosure is incorporated herein by reference thereto. Each of these box blanks, which are die-cut into a sheet, generally has six faces of a box, and some edges are completed with gluing or closing flaps or tongues. Preferably, the waste bits, i.e., the unused area of the sheet either between the tongues or between the blanks, are immediately stripped after the cutting action in order to leave, in the outlet pile, only finished blanks connected to each other by some nicks.
The die-cutting machine usually includes an infeed station in which the sheets are seized one-by-one from the top of a pile previously arranged and then carried onto a feeding table. On this feeding table, every sheet is aligned on front lays and side marks prior to being seized on a front edge of the sheet by a series of grippers which are mounted on a crossbar, whose two ends are attached to endless chains which transfer the bar and the sheet through the various stations of the device. Thus, a sheet will be transferred into a die-cutting station which includes a platen press provided with cutting blades and then to a waste stripping station, which is usually followed by a delivery station in which the sheet stripped of the waste is deposited into a stack of sheets of cut blanks. If desired, a printing station may be provided preceding the die-cutting station.
In the waste stripping station, the sheet is carried flat onto a horizontal board which is perforated according to the circumference of the waste bits to be stripped from the sheet. A horizontal upper stripping tool, which has a shape of a frame provided with crossbars supporting stripping pins or ejectors and/or pressers, is moved in a vertical direction. Beneath the perforated board is located a second horizontal stripping tool also having the shape of a frame supporting vertical telescopic pins arranged in correspondence with the upper ejectors or pins. The ends of the telescopic pins arrive in the aperture of the board slightly above the upper plane. Thus, when the upper tool is lowered onto a positioned die-cut sheet, the combination of the respective ejectors and telescopic pins pinch the waste bits and take them downward through the board and then they are dropped into a container. An example of this type of stripping station is disclosed in U.S. Pat. No. 3,786,731, whose disclosure is incorporated herein by reference thereto.
For rigidity purposes, the bars carrying the grippers are either full or made of profiled bars having a minimum thickness of 10 millimeters, and the thickness is usually in a range of 10 and 30 millimeters. Thus, if the grippers are high, i.e., they held the sheet at a level of the upper face of the bar, it is necessary to additionally shift the board and the lower tool, on the one hand, in a vertical alternating descending motion in order to let the gripper bar pass through and, on the other hand, in an ascending motion in order to support the sheet in its travelling direction.
However, an accurate and repetitive motion in the vertical translation of a board of a horizontal frame can be ensured only by acting simultaneously on its four corners. Thus, a current stripping station includes three sets of individual tools driven in translation, which fact necessitates a mechanism particularly heavy and of high inertia which will consume a lot of energy.
Moreover, the vertical motion of the tool causes important eddy currents of air within the station which have a pernicious influence on the accurate positioning of the sheet which is fragile because of the die-cutting operation.